Prediction of quenching residual stress of Al-Zn-Mg-Cu alloy during quenching and cryogenic treatment

Al-Zn-Mg-Cu alloys are widely used in the aerospace industry due to their excellent properties. The majority of heat-treatable aluminum alloys are treated sequentially by solution, quenching and ageing, which gains a good combination of properties by precipitating secondary phases from supersaturated solid solution matrix. As a result of the different levels of thermal expansion and cold contraction of the sample during rapid cooling, a high level of residual stresses is generated. Residual stress can induce distortion during subsequent machining. However, the degree of residual stress reduction during aging treatment is limited. In recent years, cryogenic treatment is adopted to reduce the residual stress. The stress-strain relationship of materials at cryogenic temperatures is one of the most critical parameters determining the accuracy of simulation results. Therefore, this work investigates the stress-strain relationship of Al-Zn-Mg-Cu alloy at different cryogenic temperatures as well as strain rates, and establishes a cryogenic constitutive equation according to the Arrhenius model. The residual stress distributions of the sample after different treatments is predicted with and without the cryogenic temperature constitutive, respectively by the method of finite element simulation. The simulation results are also compared with the experimental measurements, which proves that the cryogenic temperature constitutive equations are essential for the accuracy of the finite element simulation results.

Key words: Residual stress, Cryogenic treatment, Quenching, Constitutive equation, Al-Zn-Mg-Cu alloy